Sensitizing of silver-halide emulsions



Jan. 4, 1938. w. zE-H 2,104,054

SENSITIZING OF SILVER HALIDE EMULSIONS Filed oct. 1o, 1932 In vh for Patented Jan. 4, 193s UNITED STATES' SENSITIZING OF SILVER-HALIDE -EMULSIONS Walter Zeh, Dessau in Anhalt, Germany, assignor to Agfa Ansco Corporation, Binghamton, N. Y., a corporation of New York Application October 10, 1932, Serial No.`637,131 In Germany July 28, 1931 7 Claims.

My present invention relates to sensitizing of photographic' emulsions.

lOne of its objects is to provide such an emulsion the sensitiveness of which is raised over the range of wavelengths to which the emulsion is normally sensitive. Further objects will be seen from the detailed specification following hereafter. Reference is made to the accompanying drawing which instances the spectral region to which a silverhalide gelatin emulsion sensitized by my new dyes is sensitive and part of the individual sensibility of the vused emulsion. v

I have found that a silver-halide emulsion containing a cyanine dye of the general formula:

V'=H, alkyl, OHMoXalkyl, substituted amino groups, beni@ e,

y=S, Se, CH=CH, O, C(CH3)2 (in the case of y being CH=CH, the polymethenyl chain may also be linked in para-position to the nitrogen vatom of the heterocveir. nuclei),

r=alkyl,

n- 42 or 3, X=ha1ide, perchlorate, paratoluene sulfonate, al-

kylo-sulfate, nitrate,

at least one carbon atom of the'polymethenyl chain connecting the two heterocyclic nuclei being linked to an alkyl group, the remaining carbon atoms of thechain being linked to hydrogen, is sensitive to the red and infrared region of the spectrum apart from its individual sensitiveness.

Photographic silver halide emulsions sensitized in accordance with the invention attains a quite remarkable sensitiveness to the region of the spectrum comprising waves of about 550 to w50/nl. The pentamethinecyanines (n in Forumla l being 2). impart to a silver-halide emulsion containing them a range of sensitivity extending, from Wave lengths of about 550 to 950ML and the -heptamethin-e cyanines (n in Formula 1 being 3) impart to such an emulsion a range of sensitivity from about 650 to 105mm. It will be seen that a prolongation of the polymethenyl chain causes a displacement of the range of sensitivity towardsv the region of longer wave lengths.

In the aforesaid general Formula 1 y may represent sulfur, selenium, the vinyl group CH=CH, oxygen or C(CH3) z. V may take any position in the benzene nuclei, however, the 5 and 6 positions, and the 5 and 6 positions are preferred. In the case y being CH=CH the 6 and 7, and 6 and 7 5 positions are preferred. V may represent an alkyl group such as methyl, ethyl, etc. or an alkoxyl group, for-instance, a. -methoxy or ethoxy group, or halide, or benzene or a substituted amino group, for instance, acylated amino groups or OH. r may be alkyl, for example, methyl, ethyl, propyl etc. X can be any suitable anion that will precipitate the dye, for instance, a halide,v paratoluene sulfonate, alkylosulfate, perchlorate, nitrate or the like. The benzene nuclei may contain one or more of the substituents enumerated. The polymethenyl chain may be substituted by one or more alkyl groups, for instance, methyl groups. y

The different radicals indicated for y in Formula 1 cause a different sensitizing region of the dye, the remaining composition of the molecule being the same. Thus, for instance, the introduction of selenium or the vinyl group CH=CH into the molecule instead of sulfur causes a displacement of the range of sensitivity towards `the region of longer Wave length.

In the accompanying drawing there are reprolduced 4 spectrograms of the same silver-bromide gelatin emulsion containing about 4 per cent of silver-iodide sensitized with different dyes as as follows:

Fig. 1 with bis-[3-ethyl-benzthiazole-(2) l-'ymethyl-pentamethinecyanine iodide;

Fig. 2 with bis-[3-ethyl-{naphtho-2.1:4.5- thiazole (2) l -methylpentamethine-cyanine iodide: Fig. 3 with bis-[3-ethyl{naphtho-2.1':li.5l thiazole (2) l methyl heptamethine cyanine iodide. 1

The curves represent the range of sensitiveness of the sensitized emulsion in relation to its individual sensitivity, that is to say if the exposure of the emulsion had been prolongated the blackened area of both the curves shown in one graph would have been increased.

In the spectrograms the abscissae are graduated in millimicrons (at) while the ordinates are graduated in divisions denoting the blackening of the tested film. The lblackening is taken by exposing the lm in a diffraction grating spectrog'raph of Carl Zeiss, Jena,v provided with a `Rowland diffraction grating, while illuminating with. a 10Q Watt nitra lamp through a stage slot.

If the sensitizing maximum of the sensitized region of the emulsion lies at wave lengths over 800ML, the camera is adjusted vin such a manner that it sweeps over a range of wave lengths extending from about 600ML to about 110D/rp., the camera being provided with an Agfa red lter No. 42 in order to screen off the spectra of a higher order. The stage slot has 6 stages and exposure is thus effected so that the 6th stage is just visible in the standard sensitiveness of the emulsion or in the range of sensitiveness im'- parted to the emulsion by the sensitlzer if the camera is turned.

The dyes are obtainable according to the desired solubility in form of the bromide, iodide, perchlorate etc., and are used in a quantity such as is usual for the known sensitizing dyes. This quantity may amount to about 0.5 to 2 milligrams per 1 kg. of emulsion ready for being cast which contains about 9 per cent of gelatin, 4.5 per cent of silver-halide and the rest water. However, I do not wish to limit my invention to the quantities just indicated, the most suitable amount will in each case be lfound by a few comparative experiments. The dyes may be added to the emulsion in form of solutions. Suitable solvents are the alcohols, for instance, methyl or ethyl alcohol which may be used anhydrous or diluted with water. The dyes are applied to the emulsion during any stage of its production, however, they are preferably added to the finished emulsion before casting.

The dyes may likewise be incorporated in the' emulsion by coating the cast, but not dried, emulsion layer with a solution of the sensitizer in, for instance, aqueous or nonaqueous methyl alcohol or ethyl alcohol, applied by means of a coating roller. The concentration of the solution depends upon the speed of coating; for example, when the speed of coating amounts to 20 cm. per second, a suitable solution may consist of about 1 mg. of the sensitizer dissolved in 100 cc. of

aqueous methyl alcohol of 50 per cent strength.

Another method of incorporating the sensitizer in the emulsion consists in bathing the finished photographic material in a bath in which the dye is dissolved. Such a treatment may be as followst-The photographic material to be sensitized is bathed in a solution containing 1 milligram of bis- [3-ethy1{naphtho2.1 :3.4-thiazole 1- (2) l--methyl-pentamethinecyanine iodide in 500 to 1000 cc. of an aqueous solution of methanol of 50 per cent strength for about 5 minutes. The material is then dried, whereupon it is ready for use.

The dyes are suited for sensitizing an emulsion made according to the boiling process as well as for sensitizing an emulsion made according to the ammonia process.

The production of the pentacarbocyanines is analogous to methods disclosed in U. S. Patent 1,524,791 and the heptacarbocyanines are produced analogous to methods disclosed in German Patent 499,967 and will more clearly result from the following examples. The preparation of those of the bases serving as a starting material for the production of the dyes which have not yet been described in literature is analogous to that of the known bases.

The preparation of the substitutedbenzthiazoles may start from the correspondingly substituted r amino-benzenes, `which are converted by means of aceticl anhydride into their acetyl compound.

This latter is converted, according to the method of Jacobson and Sllwald (Berichte der Deutschen Chemischen Gesellschaft, vol. 21, page 2627) into the thioacet-compound by means of phosphorus-pentasulflde. By oxidation with potassium ferricyanide in alkaline solution the substituted benzthiazoles are obtained.

For the production of the 2methylbenzselen azoles substituted in the benzene nucleus which do not appear to have been yet described, the zinc salt of a correspondingly substituted orthoamino-seleno-phenol of the formula =alkyl, oxalkyl, substituted amino-groups, halogen is boiled with acetic anhydride, or a disubstituted ortho-diamino-diphenyl-diselenide of the formula is boned wxthjaceuc acid with addition of zinc dust.

Thus, for instance, for the production of 5-'ethoxy-2-methyl-benzselenazo1e, the l-amino- 2-nitro-4-ethoXy-benzene is converted according to the method of Bauer (Berichte der Deutschen Chemischen Gesellschaft, vol. 46, 1913, pages 2 grams of 2-methyl-benzthiazole-ethyl-iodide and 1 gram of -ethoxy-a-methyl-acrolein-acetal areheated in 5 cc. of dry pyridine for 30 minutes to 130 C. On addition of water the dye separates from the blue solution in form of green flakes. Recrystallization from alcohol yields green rods.

The alcoholic solution of the dye shows an absorption maximum at a wave length of about 650ML.

Incorporated in a silver-bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to it a range of sensitiveness from about 550 to 750ML with a maximum at about 695ML.

Eample 2,-In a manner analogous to Examiodide corresponding with the formula:

by starting from 2methyl-benzselenazole-ethyiiodide. The dye crystallizes from alcohol in bright green needles.

The alcoholic solution of the dye shows an absorption-maximum at a wave length of about 668/142. Y

Incorporated in a silver-bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to it a range of sensitiveness from about 580 to '760ML with a maximum at about 705ML.

Example 3.--By heating 3 grams of 2methyl6 acetyl-amino-benzthazole-diethylsulfate with 2 grams of -ethoxy-a-methylacrolein-acetal in 10 cc. of pyridine to 130 C. the dye bis-[3-ethyl-6- acetylamino benzthiazole- (2) l-'y-methyl-pentamethinecyanine monoethylsulfate corresponding with the formula is obtained in form of green needles,

The alcoholic solution of the dye shows an absorption maximum at a wave length of about 670m.

Incorporated in a silver-bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to it a range of sensitiveness from about 580 to 800ML with a maximum at about 715ML. 'I'he 2methyl6acetylaminobenzothiazole whose diethyl sulfate is used in this example may be made by acetylating the 2-methyl-6-aminobenzothiazole described in the application Ser. No. 590,940.

Example 4.-The dye bis-[3-ethyl-{naphth'o- 2'.1' :4.5-thiazole (2) l--methyl pentamethinecyanine iodide corresponding with the formula:

is obtainable by heating 2 grams of 2-methyl-- naphthothiazole-ethyl-iodide with 2 grams of ethoxy--methylacrolein-acetal in 5 cc. of dry pyridine for about 15 minutes to 130 C. 4From the greenish brown solution the dye precipitates in form of a black powder on addition of Water.,

The dye is separated by iiltration, washed with acetone and recrystallized from alcohol.

'I'he alcoholic solution of the dye shows an absorption maximum at .a wave length of about 690ML.

Incorporated in a silver bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to it a range of sensitiveness from about 600 to 780W. with a maximum at about 730W.

Example 5.-When YVusing in Example 4 2- methyl-benz-selenazole-ethyl-iodide instead of` 2 methyl--naphthothiazole-ethyl iodide, the

dye bis- [3-ethyl-ben2selenazole- (2) l--methylpentamethinecyanine iodide corresponding with the formula:

is obtained. The dye crystallizes from alcohol in form of a green crystal powder.

The alcoholic solution of the dye shows an absorption maximum at a wave length of about 665ml. f

Incorporated in a silver-bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to ita range of sensitiveness from about 580 to '760ML with a maximum at about 705W..

Example 6.--For producing the dye bis-[3- ethylbenzthiazole (2)] ,6.1-- dimethyl-pentamethinecyanlne iodide correspondingnwith the formula:

2 grams of 2methyl-benzthiazole-ethyl-iodide and 1 gram of -ethoxy-a.pdimethyl-acrolein acetal are heated in 5 cc. of pyridine for 10 min-v utes to 140 C. On addition of 5 cc. of an aqueous solution of potassium iodide of about 10 per cent strength the dye separates from the blue solution in pyridine in form of lustrous green thin plates.

'Ihe alcoholic solution of the dye shows an absorption maximum at a wave length of about 660ML.

Incorporated in a silver-bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to it a range of sensitiveness from about 560 'to 760ml with a maximum at about 700ML..

Example 'l'.-The dye bis-[3-ethyl-benzthiazole- (2) l--methyl-heptamethinecyanine iodide corresponding with the formula:

is obtainable by adding 0.25 cc. of diethylamine to a boiling mixture of 2 grams of Z-methyl-benzthlazole-ethyl-iodide and 1 gram of e(naph pentadiene-hydrochloride in 5 cc. of alcohol and continuing with heating for about 10 minutes, whereupon the dye precipitates from the solution which has a bluish green color, in the form of dark-green thin plates having a metallic lustre.

Incorporated in a silver-bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to it a range of sensitiveness from about 650 to 900ml with a maximum at about 815ML.

Example 8.-For producing the dye bis[3 ethyl -f6 diethyl amino benzthiazole (2) methyl-heptamethinecyanine perchlorate corresponding with the formula a mixture of 2 'grams of 5diethylamino2 methyl-beninthiazole-ethyl-iodide and 1 gram of f-phenylimido-a phenylamino ('y-methyl asypentadiene)hydrobromide in 10 cc. of alcohol is heated until boiling, and to the boiling` mixture there is added l cc.' of diethylamine. Heating is continued for about 10 minutes until the solution assumes a deep green color, there are then added 2 cc. of an aqueous solution of sodium perchlorate of about 10 per cent strength and a small quantity of ether. The dye separates in the form of thin plates having coppery luster. After ltration and thoroughly washed with acetone the dye is recrystallized from methanol. Incorporated in a silver-bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to it a range of sensitiveness from about 650 to 950W with a maximum at about 830ML.

Example 9.-The dye bis-[3-ethyl- {naphtho- 2' .1' :4.5-thiazole (2) l--methyl -heptamethinecyanine iodide corresponding with the formula:

S S l B'. H II CH3 H H H E 2 pery luster.

2 grams of lepidine-methyl-iodide and 1 gram of e-phenylimido-a-phenylamino-(y-methyl-a.-/ pentadiene hydrobromide in 10,cc. of alcohol are heated to boiling and the boiling solution is mixedwith 0.2 cc. of dimethylamine. Heating is continued until the mixture assumes a darkgreen color, there are then added 2 cc. of an aqueous solution of sodium perchlorate Vof about per cent strength. On cooling the dye precipitates on the Walls of the vessel as a coating having a coppery luster.

Incorporated in a silver-bromide emulsion containing about 4 per cent of silver-iodide the dye imparts to it a range of sensitiveness from about '700 to 105mm with a maximum at about 960ml, which however, is not sharp.

a (-naphthylimino) e naphthylamino) amethyl-a.v-pentadiene -hydrochloride may be made according to Knig, Journal fr praktische Chemie, vol. 69, page 136, from -naphthylamine, a-picoline and cyanous chloride in etheric solution. In an analogous manner e-phenylimido-a-phenylamino-y-methyl-axypentadienehydrobromide is obtained from cyanous bromide, aniline and y-picoline.

Example 1 1 .--bis- [B-methyl-benzthiazole- (2) la.e-dimethyl-pentamethinecyanine iodide corresponding with the formula:

is obtainable by heating 2 grams 2-ethy1-benzthlazole-methyl-iodide with 1 cc. of -ethoxyacrolein-acetal in 5 cc. of pyridine for about 15 minutes' to about 130 C. From the dark-green reaction mixture the dye precipitates in the form of blue-green flakes on addition of water. By recrystallization of the crude material from methanol there are obtained steel-blue, felted needles.

' Thealcoholic solution of the dye has an absorption maximum at about 665ml.

By incorporating the dye in a silver-halide emulsion the latter acquires a sensitivcness to waves from about 610ML to 760W with a maximum at about 715ml.

It is to be understood that my invention is not limited to the foregoing examplesl or to the specific details given therein. Numerous other embodiments are possible and I contemplate as included within my invention all such modications and equivalents as fall within the yscope of the appended claims. So, for instance, the benzene nuclei may contain one or more substituents. The nomenclature used is arbitrary, but it is familiar' to every chemist skilled in the art and has the advantage of clearness. Numbering of the thiazoles etc. commences from the sulfur etc., numbering of the quinoline nuclei and of the dyes commences from the nitrogen atom. The formulae of the dyes as given herein represent the molecular structure of my new dyes so far as known. If, however, in the future it should become evident that the formulae do not exactly correspond to the dyes, this fact will not affect my invention since the dyes will be easily identimethinecyanine the pentamethenyl chain of iied by the methodof producing the same which has been fully described in the examples and is analogous to known methods.

What I claim is:

1. A photographic material comprising a silverwhich is substituted by an alkyl group.

3. A photographic material comprising a silverhalide emulsion containing bis-[3-ethyl-benzthiazole- (2) l -v-methyl-pentamethinecyanine iodide.

4. A photographic material comprising a silverv halide emulsion containing bis-y 3-ethy1-benzselenazole- (2) l--methyl-pentamethinecyanine iodide.

5. A photographic matrial comprising a silverhalide emulsion containing a sensitizing material which comprises a pentamethinecyanine, the pentamethenyl chain of which is substituted by an alkyl radical.

6. A photographic material comprising a silverhalide emulsion containing a sensitizing material which comprises a pentamethinecyanine, the pentamethenyl chain of which is substituted by a methyl radical. y

7. A photographic material comprising a silverhalide emulsion containing bis-[3.-ethy1-6-acetylamino-benzthiazole (2)] ymethylpentameth inecyanine-monoethylsulfatef WALTER ZEH. 

